The Road to Uniform Plasma Etching of Printed Circuit Boards

Early in AT & T Bell Laboratories' involvement with plasma smear removal for multilayer boards, the generic problem of uniform etching over large size panels became obvious. Techniques were developed which provide a quantitative measurement of the etch uniformity. These techniques were used to evaluate the etch performance of existing reactors and as an aid in developing a better understanding of the factors which influence etch uniformity. This characterisation procedure enabled the development of new reactor geometries which greatly improved etch uniformity as compared to previously used configurations. This paper describes these steps along the road to uniform etching of printed circuit boards.